The preparation of poured concrete structures is a well known art that has been developed for many years. The preparation of hollow reinforced concrete shapes having smooth precise holes through the walls thereof is a difficult task. One method in use today is to mold the hollow shape and subsequently bore the hole with a diamond tooth drill. This is extremely expensive. Another procedure is to employ a core for the hole and mold the entire structure in one operation. The surface smoothness and precision of the hole size depends on the core and material from which it is made. A core having a polished steel surface is very expensive and the surface deteriorates after being reused a few times, causing the cored hole not to have the desired smoothness and to make the core more difficult to remove with each reuse. Cores made of other materials, such as fiber glass, polyvinyl chloride, rubber, or aluminum, have the same or similar problems of surface deterioration. As the core surface deteriorates it becomes pitted and more and more difficult to remove until it must be hammered out of the concrete structure after the removal of all the outside forms and central core used in preparing a structure. When such a hole core is hammered out of its position the core is frequently damaged or destroyed, usually accompanied by severe damage to the surface of the hole to the extent that precision fittings cannot be applied to the hole. The labor cost of using such cores, and the replacement cost of cores that can only be used a few times results in inordinately high prices for such concrete structures.
It is an object of this invention to prepare a poured reinforced concrete hollow shape having at least one hole through a wall of the shape by using a form in which the core for the hole is readily removed from the solidified shape, leaving a hole with a smooth surface and a precise size.